In general, an organic light emitting phenomenon refers to a phenomenon in which electric energy is converted into light energy of an organic material using an organic material. An organic electronic element utilizing the organic light emitting phenomenon usually has a structure including an anode, a cathode, and an organic material layer interposed therebetween. In many cases, the organic material layer may have a multilayered structure including multiple layers made of different materials in order to improve the efficiency and stability of an organic electronic element, and for Embodiment, may include a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, or the like.
A material used as an organic material layer in an organic electronic element may be classified into a light emitting material and a charge transport material, for Embodiment, a hole injection material, a hole transport material, an electron transport material, an electron injection material, and the like according to its function. Further, the light emitting material may be divided into a high molecular weight type and a low molecular weight type according to its molecular weight, and may also be divided into a fluorescent material derived from electronic excited singlet states and a phosphorescent material derived from electronic excited triplet states according to its light emitting mechanism. Further, the light emitting material may be divided into blue, green, and red light emitting materials, and yellow and orange light emitting materials required for better natural color reproduction according to its light emitting color.
Currently, the power consumption is required more and more as the size of display becomes larger and larger in the portable display market. Therefore, the power consumption is a very important factor in the portable display with a limited power source of the battery, and efficiency and life span issue also is solved.
Efficiency, life span, driving voltage, and the like are correlated with each other. For Embodiment, if efficiency is increased, then driving voltage is relatively lowered, and the crystallization of an organic material due to Joule heating generated during operation is reduced as driving voltage is lowered, as a result of which life span shows a tendency to increase. However, efficiency cannot be maximized only by simply improving the organic material layer. This is because long life span and high efficiency can be simultaneously achieved when an optimal combination of energy levels and T1 values, inherent material properties (mobility, interfacial properties, etc.), and the like among the respective layers included in the organic material layer is given.
In general, an electron transferred from an electron transport layer to a light emitting layer and a hole transferred from a hole transport layer to the light emitting layer are recombined to form an exciton.
However, the hole moves faster than the electron, and the exciton formed in the light emitting layer moves int the electron transport layer, causing the charge unbalance in the light emitting layer, resulting the emission of light in the interface of the electron transport layer.
When light emission occurs in an interface of the hole transporting layer, the organic electroluminescent device suffers from the disadvantage of a reduction in color purity, and efficiency. Especially, high-temperature stability deteriorates at the time of manufacturing an organic electronic element, resulting in a short lifespan of the organic electronic element. Therefore, the development of an electron transport material having improved hole blocking ability while having high-temperature stability and high electron mobility (within the driving voltage range of a blue element of the electron mobility full device is needed (Adv. Funct. Mater. 2013, 23, 1300023).
When only one material is used as a light emitting material, there occur problems of shift of a maximum luminescence wavelength to a longer wavelength due to intermolecular interactions and lowering of the efficiency of a corresponding element due to the deterioration in color purity or a reduction in luminous efficiency. On account of this, a host/dopant system may be used as the light emitting material in order to enhance the color purity and increase the luminous efficiency through energy transfer. This is based on the principle that if a small amount of dopant having a smaller energy band gap than a host forming a light emitting layer is mixed in the light emitting layer, then excitons generated in the light emitting layer are transported to the dopant, thus emitting light with high efficiency. With regard to this, since the wavelength of the host is shifted to the wavelength band of the dopant, light having a desired wavelength can be obtained according the type of the dopant.
However, only the introduction of hosts/dopants cannot maximize efficiency, and the maximal efficiency can be attained by characteristics exhibited from a combination of core and sub-substituents of the light emitting material and an optimal combination of host/dopants.
That is, in order to allow the organic electronic element to sufficiently exhibit excellent characteristics, most of all, materials constituting an organic material layer in the element, for Embodiments, a hole injection material, a hole transport material, a light emitting material, an electron transport material, an electron injection material, and the like need to be supported by stable and efficient materials, but the development of stable and efficient materials for the organic material layer for an organic electronic element is not sufficiently achieved. Therefore, the development of new materials is continuously required, and especially, the development of an electron transport material and a light emitting material is urgently required.